I'm building a Scarab Trimaran.
Working on the rudder atm, and it requires a SS Tube, 33,8mm OD, 6,35mm wall.
As a privat person, I cant get these dimensions in the length I need (I need like 1200mm, minimum amount I can buy is 6meters, which would be a bit costly)
Question now is, does a full 6061-T6 aluminium bar with dia 35mm be a good replacement for the SS bar?

Thanks

G

Yield is about 1/2 for Aluminum; weight is about 1/3. Personally, I would use SS. Even if the aluminum bar is solid, not much additional strength is realized. The moment of inertia (in^4) is proportionate to the power of the radius. Adding material back in to decrease the ID has little effect.

Except for cost, itanium would be better than stainless, as it does not corrode in seawater, unlike stainless, which has other problems, especially when welded and sealed off from oxygen.

__________________

__________________1st rule of yachting: When a collision is unavoidable, aim for something cheap.
"whatever spare parts you bring, you'll never need"--goboatingnow
"Id rather drown than have computers take over my life."--d design

Assuming I did the math correctly (always an issue) this tube has a metal volume of 21.35cubic inches

If we make it out of red brass that's 6.38lbs, or about $12
If in titanium it's 3.5lbs or $19.
316 stainless its 6.19lbs or $4.76

Somehow I don't think scrap prices are really relavent to what we are talking about here.

The problem with titanium is not price, it's stiffness. The tube would need to have a substantially larger OD than stainless to work the same. Which of course negatively effects the thickness of the foil necessary to contain it. Admittedly its corrosion resistance can't be touched. Except by carbon fiber which also wins on weight and stiffness.

__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.

I'm building a Scarab Trimaran.
Working on the rudder atm, and it requires a SS Tube, 33,8mm OD, 6,35mm wall.
As a privat person, I cant get these dimensions in the length I need (I need like 1200mm, minimum amount I can buy is 6meters, which would be a bit costly)
Question now is, does a full 6061-T6 aluminium bar with dia 35mm be a good replacement for the SS bar?

I don't know how pipe is specified in metric using countries. If it's specified in inches, look for it in the above terms from industrial supply places. Or else ask McMaster-Carr above to ship you a piece, they're experienced at shipping worldwide. They can cut to your length, and ship that. And never mind all this baloney.

Stumble-
Until the collapse of the USSR (world's primary source of titanium) it was a "strategic material" and you could pretty much only dream about it. So titanium "now" is dirt cheap by comparison. I understand the USSR actually made one (two?) nuclear sub with a titanium hull--even the US couldn't afford to do that, then or now.
But.
There are four primary titanium alloys used, you aren't pricing pure titanium, you need alloy quotes.
And titanium is a b|tch to machine, it eats machine tools the way good teak eats cheap blades. Which also means a lot of machinists hear the word "titanium" and run like vampires at a garlic fest.
And then you've got to find rod stock or tube stock, not just ingots. Unless you really want to generate lots of your own scrap. How many places compete for that market? In what volume? Ka-ching!

Nah, the stuff is still just wrapped in extra costs. If you think finding a "welding shop" that can simply do a good job on stainless tubing for a pulpit isn't easy...just try finding anyplace that deals in the titanium stock, even if you're planning to "just" bolt it in place.
Great stuff but like who was it said about yachts? If you have to ask the price, you can't afford it.

BTW, Titanium is about 1/2 the weight of stainless, and virtually as strong.

__________________1st rule of yachting: When a collision is unavoidable, aim for something cheap.
"whatever spare parts you bring, you'll never need"--goboatingnow
"Id rather drown than have computers take over my life."--d design

Off hand I can think of three places that I can get quality Titanium work done locally, and one U.S. Manufacturer targeting mass produced titanium parts. Having worked in the industry for two years I probably know a good bit more about it than most.

Any welder than can do decent stainless or aluminium welding can do titanium work as well, it just requires a backside argon shield. Fabrication is trickier due to its strength and kickback, but machining it's all that bad. Normal metal working tools work just fine, with lots of cutting oil (refined olive oil works best) and slow speeds.

The U.S. historical price on titanium was driven by poor US policy. Because it was a strategic metal the military could only buy it from US sources, and monopoly preventions were waived. So the major U.S. titanium supplier bought out all the rest, and ensured there was no other manufacturer to compete with them. Then they never reduced prices after better refining techniques took over the industry and costs plummeted.

Right now the cost of titanium has been in a downward spiral for years as usage grows and mills can ramp up production. Long term industry estimates predict this will continue for a number of years. And at least for US users it is happening pretty fast. right now the major cost driver isn't production it is in the distribution end. With suppliers charging 100 times their cost for a part (McMaster Carr is the biggest culprit).

But new suppliers are starting to stock titanium fasteners (Ace Hardware, Fastenal) which will help a lot in market penetration. Once people start seeing that it doesn't have to be expensive they will start demanding it elsewhere.

Just as an example, ronstan charges I think $75 for a lifeline stantion, Gurhauer charges $50, and Allied Titanium charges $60 for a titanium (G2) or $80 for G5.

__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.